EP1173945A1 - Architecture bidirectionnelle de reseau dwdm presentant une augmentation de capacite et un systeme d'empilage de frequences - Google Patents

Architecture bidirectionnelle de reseau dwdm presentant une augmentation de capacite et un systeme d'empilage de frequences

Info

Publication number
EP1173945A1
EP1173945A1 EP00922286A EP00922286A EP1173945A1 EP 1173945 A1 EP1173945 A1 EP 1173945A1 EP 00922286 A EP00922286 A EP 00922286A EP 00922286 A EP00922286 A EP 00922286A EP 1173945 A1 EP1173945 A1 EP 1173945A1
Authority
EP
European Patent Office
Prior art keywords
signals
dwdm
headend
primary
passbands
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00922286A
Other languages
German (de)
English (en)
Inventor
Robert Howald
Shlomo Ovadia
Timothy Brophy
Curtiss Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Arris Technology Inc
Original Assignee
Arris Technology Inc
General Instrument Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arris Technology Inc, General Instrument Corp filed Critical Arris Technology Inc
Publication of EP1173945A1 publication Critical patent/EP1173945A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/2801—Broadband local area networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0226—Fixed carrier allocation, e.g. according to service
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0228—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths
    • H04J14/023—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON]
    • H04J14/0232—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON] for downstream transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
    • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
    • H04J14/0245—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU
    • H04J14/0246—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU using one wavelength per ONU
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
    • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
    • H04J14/0249—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU
    • H04J14/025—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU using one wavelength per ONU, e.g. for transmissions from-ONU-to-OLT or from-ONU-to-ONU
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0282—WDM tree architectures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0283—WDM ring architectures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0286—WDM hierarchical architectures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/03—WDM arrangements
    • H04J14/0305—WDM arrangements in end terminals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/21—Server components or server architectures
    • H04N21/222—Secondary servers, e.g. proxy server, cable television Head-end
    • H04N21/2221—Secondary servers, e.g. proxy server, cable television Head-end being a cable television head-end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client 
    • H04N21/61—Network physical structure; Signal processing
    • H04N21/6106—Network physical structure; Signal processing specially adapted to the downstream path of the transmission network
    • H04N21/6118—Network physical structure; Signal processing specially adapted to the downstream path of the transmission network involving cable transmission, e.g. using a cable modem
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client 
    • H04N21/61—Network physical structure; Signal processing
    • H04N21/6156—Network physical structure; Signal processing specially adapted to the upstream path of the transmission network
    • H04N21/6168—Network physical structure; Signal processing specially adapted to the upstream path of the transmission network involving cable transmission, e.g. using a cable modem
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
    • H04N7/17309—Transmission or handling of upstream communications
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/22—Adaptations for optical transmission

Definitions

  • the present invention relates generally to a cable television hybrid-fiber-coax (CATV HFC) architecture that provides increased capacity in the reverse path of the network. More particularly, it describes an architecture that incorporates multiplexing, both optical multiplexing, using dense wave division multiplexing (DWDM), and RF multiplexing, using frequency stacking, so as to increase the efficiency of the return path.
  • CATV HFC cable television hybrid-fiber-coax
  • downstream content occupies the 50-870 MHz frequency partition of the network.
  • the return path signals are relegated to the 5-42 MHz frequencies (of course those skilled in the art will appreciate that although the typical reverse path frequency band in the United States is 5-42 MHz, overseas the range varies and may be 5-85 MHz - the concepts discussed herein are not to be interpreted as being limited to the current US range). Given the asymmetrical nature of the frequency bands used it is very likely that the reverse path traffic will be the first to be constrained.
  • DWDM systems have been deployed to provide segmentation and increased bandwidth.
  • DWDM can add impairment that was not present in the system earlier.
  • multiplexing in the RF domain using frequency stacking has been used in the reverse path passband to increase bandwidth efficiency. That is, the implementation of a frequency stacking system expands the return bandwidth per home passes and allows for larger node sizes, thereby reducing the overall system costs. Again, however, by itself frequency stacking can add impairment to the system.
  • the present invention is therefore directed to the problem of developing an architecture that meets the current needs of multiplexed analog and digital systems, segments the forward signal to address individual subscribers and increases bidirectional capacity without the use of additional fiber.
  • the present invention provides a hybrid DWDM with frequency stacking architecture that solves the current needs of muliplexed analog and digital systems to provide maximum capacity based on two-way interactive data communications.
  • a CATV architecture provides increased capacity in the reverse path network for two-way cable communication and includes a plurality of optical-to-electrical conversion nodes, a primary/secondary headend, and a master headend.
  • the primary/secondary headend interconnects the optical-to-electrical conversion nodes and master headend.
  • the nodes and primary/secondary headend together includes an upconverter for receiving a plurality of RF reverse path passbands from a plurality of coax legs and upconverting the return passbands to different passbands, a plurality of DWDM transmitters, each transmitter having an output on the ITU grid and transmitting a concentration of discrete passbands and a DWDM multiplexer, receiving a signal from each of the plurality of DWDM transmitters and optically multiplexing the DWDM transmitters on a single fiber, the multiplexed signals being routed to the master headend.
  • an upconverter for receiving a plurality of RF reverse path passbands from a plurality of coax legs and upconverting the return passbands to different passbands
  • a plurality of DWDM transmitters each transmitter having an output on the ITU grid and transmitting a concentration of discrete passbands
  • a DWDM multiplexer receiving a signal from each of the plurality of DWDM transmitters and optically
  • the master headend includes a DWDM demultiplexer for demultiplexing the received signals from the DWDM multiplexer into individual wavelengths, a plurality of block conversion receivers (BCRs) for receiving the individual wavelengths and converting the signals into composite RF signals and a plurality of block downconverters (BCDs) for receiving the composite RF signals from the BCRs and converting the signals into individual RF signals.
  • the individual RF signals output from the plurality of BCDs correspond to the plurality of coax legs at each optical-to-electrical conversion node.
  • Another aspect of the invention incorporates an optical amplifier, at the primary/secondary headend, that amplifies the multiplexed signals output from the DWDM multiplexer before being routed to the master headend.
  • the optical amplifier may be an erbium-doped fiber amplifier (EDFA).
  • EDFA erbium-doped fiber amplifier
  • Still yet another aspect of the invention includes using Code-Division-Multiple- Access (CDMA), Frequency-Division-Multiple-Access (FDMA), Time-Division- Multiple- Access (TDMA), or any combination thereof, to allow the transport link's available capacity, defined by channel parameters, to be achieved.
  • CDMA Code-Division-Multiple- Access
  • FDMA Frequency-Division-Multiple-Access
  • TDMA Time-Division- Multiple- Access
  • Another embodiment of the invention is directed to a method for increasing capacity in the reverse path of a two-way cable communication architecture, the architecture having a plurality of optical-to-electrical conversion nodes, a master headend, and a primary/secondary headend interconnecting the nodes and the master headend.
  • the steps of the method are as follows: receiving a plurality of RF reverse path passbands from a plurality of coax legs and upconverting the return passbands to different passbands, transmitting a concentration of discrete passbands using a plurality of DWDM transmitters, each transmitter having an output on the ITU grid, optically multiplexing the signals received from the DWDM transmitters, using a DWDM multiplexer, on a single fiber, routing the multiplexed signals to the master headend, demultiplexing the received signals into individual wavelengths, receiving the individual wavelengths and converting the signals into composite RF signals and receiving the composite RF signals and converting the signals into individual RF signals.
  • FIG. 1 depicts a typical tree-and-branch configuration of a hybrid Fiber/Coax (HFC) cable TV network architecture
  • FIG 2 depicts a DWDM subcarrier multiplexed network architecture
  • FIG 3 depicts a typical architecture for a DWDM overlay of a standard CATV distribution system
  • FIG 4 depicts a block diagram of a typical node configuration
  • FIG 5 depicts a typical frequency stacking system (FSS) block diagram
  • FIG 6 depicts a fist embodiment of an architecture according to the present invention combining DWDM and FSS technologies
  • FIG 7 depicts a first embodiment of an architecture according to the present invention combining DWDM and FSS technologies
  • FIG 8 depicts a second embodiment of an architecture according to the present invention combining DWDM and FSS technologies
  • FIG 9 depicts a third embodiment of an architecture according to the present invention combining DWDM and FSS technologies
  • FIG 10 depicts a composite RF spectrum of four upconverted return-path frequency blocks.
  • FIG 11 depicts the bandwidth expansion provided by a combined frequency stacking and DWDM return path system.
  • Typical CATV systems were almost exclusively designed for "one-way transmission" from a headend to the home. Return path implementations were typically lightly loaded and used primarily for low-speed communications with terminals or set top boxes. The recent use of DWDM in CATV was motivated by the need to significantly increase the bi-directional capacity as well as transmission access speed without adding additional fiber
  • the present invention is directed to a hybrid DWDM/FSS CATV architecture that provides increased capacity in the reverse path network. Consequently, the present invention has significantly improved the ability to handle two-way interactive multimedia communications in existing CATV systems while eliminating the need for the use of additional fiber.
  • DWDM systems in CATV today are used exclusively in the 1550 nm optical window (this wavelength window is attractive primarily due to the low fiber loss, approximately 0.22 dB/km at the 1550-nm wavelength, and the use of erbium doped fiber amplifiers (EDFA) to take advantage of the low loss).
  • the wavelengths that comprise the ITU grid are actually a set of predefined frequencies, such as the set spaced at 100 GHz, from which wavelengths can be derived.
  • the wavelength spacing is approximately 0.8 nm, and the range of wavelengths covers the EDFA band, from about 1530 to 1570 nm.
  • the spacing chosen is 200 GHz, and it is this closeness of wavelengths that make the system "dense" (this is to distinguish the DWDM systems from some existing CATV systems which use a combination of 1310 nm and 1550 nm wavelengths in a WDM arrangement).
  • the RF signals transmitted over the single-mode fiber (SMF) cables using, for example, DWDM transmitters are digital (but of course could also be analog or a combination of digital and analog) using, for example, QAM modulation.
  • the QAM channels are subcarrier multiplexed onto a particular optical wavelength (the terms QAM, digital, targeted services, or DWDM signals are frequently used interchangeably).
  • Figure 1 shows a conventional hybrid fiber/coax (HFC) cable TV network architecture.
  • the signals from the master headend 10 are connected via a "main" or “primary” fiber ring to primary/secondary headends (12a, 12b, 12c) or the secondary “hubs” in a large metropolitan area (14a, 14b, 14c and 14d).
  • the signals are transmitted over single-mode fiber (SMF) using, for example, 1550-nm externally modulated (EM) DFB laser transmitters.
  • SMF single-mode fiber
  • EM externally modulated
  • the composite signal may be, for example, a mixture of traditional broadcast analog signals with MPEG compressed digital video.
  • the optical signals may be converted to RF signals and then back to optical signals for transmission to various fiber nodes (16a, 16b, 16c and 16d) using, for example, 1310-nm DFB laser transmitters.
  • SONET Synchronous Optical Network
  • CMTSs Cable Modem Termination Systems
  • the coaxial portion of the network architecture illustrated in Figure 1, consists of, for example, RF amplifiers, taps, and coaxial cables, and spans from each fiber node (16a-d) to the corresponding subscriber's home(s), where the digital set-top box is placed.
  • Figure 2 provides an exemplary illustration of a DWDM Subcarrier- Multiplexed (SCM) network architecture for multiple AM/QAM channel transport.
  • SCM DWDM Subcarrier- Multiplexed
  • the master cable-TV headend 10 is connected via a main fiber ring to the primary headends (12a, 12b, 12c) in a large metropolitan area.
  • the analog and digital video programs at the master headend 10 are typically received via satellite and terrestrial broadcast as well as via local video servers (those skilled in the art will appreciate that the analog signals could also be "injected” or received at the primary or secondary headends).
  • Ultra-high video trunking capacity is achieved by using high- density wavelength-division-multiplexing (DWDM) and demultiplexing with cascaded Erbium-Doped-Fiber-Amplifiers (EDFA's) (23a, 23b, 23c).
  • DWDM high- density wavelength-division-multiplexing
  • EDFA's cascaded Erbium-Doped-Fiber-Amplifiers
  • the primary fiber ring multiple wavelengths in the 1550-nm band, transmitted with each wavelength a mixture of AM and digital video signals, are subcarrier multiplexed (SCM) at either passband traffic, using 64/256-QAM, or even at baseband traffic, such as OC-48.
  • the secondary fiber rings connect the various primary headends to the secondary headends.
  • a secondary fiber ring only a few wavelengths are being demultiplexed and transmitted using 1550-nm or 1310-nm laser transmitters with cascaded EDFA's.
  • the 1550-nm based broadcast traffic can be switched to a 1310-nm based traffic for both narrowcasting and broadcasting services.
  • the optical signals transmitted downstream at different wavelengths are converted back to electrical signals using optical receivers, and are transmitted to each subscriber via the coaxial cable plant.
  • Figure 3 shows a simplified master headend 300 (corresponding to reference number 10 of Figures 1 and 2) - primary/secondary headends/hubs 330 (corresponding to reference numbers 12a, 12b, 12c and 14a, 14b, 14c and 14d, respectively, of Figures 1 and 2) — and node 360 (corresponding to node reference numbers 16a-16d of Figures 1 and 2).
  • FIG. 3 is a generic architecture for a DWDM overlay of a conventional hybrid fiber/coax (HFC) cable TV network (note that for exemplary reasons only, Figure 3 assumes that the optical network remains in the 1550nm window from the master headend to the node), and includes an externally- modulated analog transmitter source 305 and a externally modulated DWDM transmitter 320 (of course, this does not have to be a DWDM externally modulated transmitter but may be a directly modulated transmitter).
  • HFC hybrid fiber/coax
  • the master headend is collectively 300
  • the primary/secondary headends/hubs are collectively 330
  • the nodes collectively 360 (individually 360a, 360b etc.) (those skilled in the art will appreciate that although illustrated as such, the ITU transmitter does not necessarily need to be co-located with the broadcast transmitter).
  • the DWDM transmitter 320 illustrated as being located at the master headend, includes laser modules for providing the bias, temperature, pre-distortion circuitry and monitoring controls as well as the means of modulating the sources with the RF content. That RF content is either the analog broadcast television signals or the targeted services QAM signal.
  • the modulation techniques are either external (using the modified balanced-bridge Mach-Zehnder interferometer) or direct (using the driving current control of the laser directly).
  • the output of analog transmitter source 305 is optically amplified 307 to a saturated level (for example, approximately +17 dBm), transmitted through 40 km of standard (non-dispersion shifted) single-mode fiber (SMF) (again, the length of the SMF is provided solely as an exemplary value) to the primary/secondary headend, amplified again by an erbium doped fiber amplifier (EDFA) 335 and split by optical splitter 340 into a number of outputs that matches the number of targeted-services wavelengths.
  • SMF standard (non-dispersion shifted) single-mode fiber
  • EDFA erbium doped fiber amplifier
  • nodes 360 are "20 km" away from the primary/secondary headend and are connected using standard SMF (note that there may be multiple nodes targeted per wavelength, especially in the early deployment stages when subscriber take rates are low corresponding to a low bandwidth requirement per node).
  • the DWDM laser sources are also externally modulated transmitters 320 in the example system, but directly modulated sources may also be used. Eight wavelengths are shown in the figure and are combined into a single fiber in a multiplexer 325 (with 200 GHz spacing, 8 wavelengths may be multiplexed).
  • the multiplexer 325 (and demultiplexer 355 described below) components are used to combine the various ITU grid wavelengths through a low loss coupler and carry them on a single fiber (and demultiplexer 355 subsequently separates those wavelengths to place them onto individual fibers).
  • the standard SMF is 40 km long, and may be distinct from the fiber carrying the analog signal, but may be in the same optical fiber cable bundle (each optical fiber cable bundle consisting of multiple optical fibers).
  • the combined wavelengths are amplified by EDFA 357 and are then demultiplexed 355 into separate fibers.
  • each targeted services wavelength is combined with one of the split analog signal outputs and distributed to nodes 360 through a single fiber carrying both the analog and digital signal.
  • the fiber node 360 contains a receiver that detects both the analog and QAM signals for distribution through the RF plant beyond the node.
  • the return path illustrated in the DWDM overlay system of Figure 3 mirrors that of the downstream path.
  • One exception to this mirroring occurs not so much in the single fiber of the DWDM system, but in the portion of the return from the node 360 to primary/secondary headend 330.
  • the return path is managed as a two-hop process.
  • a temperature compensated 1310/1550 nm laser typically a DFB
  • the time and frequency division multiplexed RF signals from each home served by this node (e.g., 1000-1200 subscribers) drive the DWDM laser 385.
  • the optical output is sent over the link (illustrated as "20 km"), to the primary/ secondary headend 330, where it is detected and amplified by a return receiver 380 before directly modulating an ITU grid DWDM laser transmitter 385.
  • the laser 385 is one of several which combine the entire return path into a DWDM set for transmission over the 40 km back to the master headend 300 and for subsequent processing.
  • Each of the DWDM wavelengths may handle the return traffic from multiple nodes 360 using a combination of time, frequency, or code division multiplexing.
  • the 5-42 MHz return passband is block upconverted or shifted to another frequency passband. This may be done in a primary/secondary headend environment or, as we will also discuss herein, in the field located node.
  • FSS frequency stacking system
  • each of the coaxial busses, RF Leg #1, RF Leg #2, etc. are RF combined into one stream.
  • An FSS approach utilizes upconversion in the node to create four passbands for the return.
  • each leg now has its own 35 MHz of space.
  • the four passbands are RF stacked and sent to the return laser.
  • Figures 5 and 6 illustrate this arrangement.
  • FIGS. 5 and 6 illustrate, there are four major components associated with a FSS system - an upconverter, a transmitter, a receiver and a downcoverter. These components would be common in function regardless of whether the application is hub or node based. Each of these components is briefly discussed below.
  • Frequency stacking begins with the upconverter 500. This device, simply put, takes multiple return passbands and shifts them to other independent passbands in the spectrum while maintaining the information that resides in the original passband.
  • each of the RF legs is upconverted to different passbands within the 50-400 MHz passband.
  • a pilot carrier serves two key functions - first, it compensates for the range of link loss introduced by the optical network, and second, it is used by the downconverter to phaselock to the upconverter thus eliminating frequency offsets.
  • the transmitter used in this application is not a standard, band-limited, return path transmitter.
  • a forward path transmitter 510 designed to operate in the 50-400 MHz passband, is used to transport the upconverted signal from upconverter 500.
  • the FSS receiver (BCR) 520 is also different than the normal return path receiver (RPR 410 of Figure 4). Again chosen for the forward path, the receiver 520 provides the composite RF output. Contained within this passband are the four upconverted bands along with the pilot carrier. To recover the individual bands, a downconversion process is performed by downcoverter 530, which provides the means of returning the upconverted bands to their original 5-42 MHz spectrum. Using the pilot carrier for frequency synchronization, the block downconverter (BCD) 530 reverses the process initiated in the node and provides four independent 5-42 MHz passbands, one for each of the upconverted bands. These outputs are then fed to the return splitting/combining network and eventually end at the individual service demodulators.
  • RPR 410 normal return path receiver
  • Figures 7-9 illustrate, respectively, first, second and third embodiments of a combined system according to the present invention.
  • Each of the approaches work together so as to increase the efficiency of both the return distribution and return transport aspects of the network and allow the combined exemplary system to have thirty-two 5-42 MHz return bands on a single fiber.
  • the main difference between the embodiments is the location of the ITU grid transmitters and the location of the frequency stacking system (the network architecture of Figure 7 has the DWDM transmitters at the primary/secondary headend, Figure 8 has the DWDM transmitters at the node and Figure 9 has both the frequency stacking system and the DWDM transmitters at the primary/secondary headend).
  • ITU grid DWDM transmitters 750 are located at the primary/secondary headend. As illustrated, this configuration upconverts the return path signals, with upconverter 766, at the node location (collectively the nodes are 760). Transmitted back to the primary/secondary headend via the optical distribution network they are received by the forward path block conversion receiver (BCR) 735.
  • BCR forward path block conversion receiver
  • the RF output is routed to a DWDM transmitter 750 which has an output wavelength on the ITU grid.
  • the specific embodiment shown in Figure 7 has a concentration of four discrete 5-42 MHz passbands on each of these transmitters (of course, those skilled in the art will appreciate that the number of passbands on each of the transmitters can be greater than the illustrative "4" passbands shown and in fact, is limited based only on how much the laser can handle).
  • the configuration of Figure 7 can optically multiplex (multiplexer 760) eight of the transmitters 750, each with its own different ITU grid wavelength, on a single fiber, providing 32 discrete 5-42 MHz passbands (1.12 GHz) on the single fiber, thereby clearly illustrating how the combination of FSS and DWDM significantly increases the reverse path traffic capacity.
  • the signals are then routed to the headend (note that depending on the distances involved, and requirements such as redundancy, optical amplifiers may be required to meet the input requirements of the headend receivers).
  • the optical signals are demultiplexed by demultiplexer 770 (in the exemplary demultiplexer shown, into the eight wavelengths). Individual wavelengths are routed to receivers (one for each wavelength) BCRs 780 which are the same type as those used to receive the frequency-stacked multiplex at the primary/secondary headend.
  • the FSS system may be completed by routing the composite RF signals from the BCRs 780 to downconverters 790.
  • the four, 5-42 MHz, RF outputs from the downconverter 790 correspond to the four coaxial legs coming into the field node 760, and may be routed to the various return path application receivers.
  • the primary/secondary or master headend receiver implementations may anticipate an RF signal in the 5-42 MHz range and may be designed to frequency convert this range of spectrum for subsequent processing, thereby requiring a downconverter component.
  • implementing these receivers instead with an input bandwidth capability that encompasses the FSS spectrum would eliminate the need for the downconverter component.
  • a more efficient implementation could accomplish this with a single downconversion placed in the receiver, using classical CATV tuner technology in front of the demodulation function in the receiver.
  • DWDM transmitters are located in the node (865 collectively in Figure 8), and are driven by the stacked RF signals. Accordingly, the individual wavelengths are transmitted back to the primary/secondary headend by ITU transmitters (866 collectively).
  • the optical signals are routed directly to multiplexers 860 (it will be appreciated that since it is possible to have different optical levels, due to different node to OTN loss budgets, some level of signal equalization may be required).
  • the output from the multiplexer 860 is sent to the master headend in the same manner as in the first embodiment.
  • the primary/secondary headend components of the second embodiment are assembled as those in the first embodiment as well.
  • Figure 9 illustrates a primary/secondary headend-based frequency stacking and DWDM system implementation.
  • both the frequency stacking system shown as a 4 or 8 band system, the details of which have been discussed earlier herein
  • the DWDM lasers 910a-d/DWDM multiplexer 920 are all located within the primary/secondary headend.
  • the outputs of the fiber nodes are received at the primary/secondary headend by dual receiver RPR/2 930.
  • the reverse path data may be aggregated to drive each DWDM laser transmitter using Frequency Stacking (FS) methods.
  • the reverse path data transmission from each subscriber is typically one of the three basic multiple access schemes — Code Division Multiple Access (CDMA), Frequency-Division-Multiple-Access (FDMA), Time-Division- Multiple- Access (TDMA), or any combination of these schemes.
  • CDMA Code Division Multiple Access
  • FDMA Frequency-Division-Multiple-Access
  • TDMA Time-Division- Multiple- Access
  • Efficient use of the reverse path link to ensure that the increased capacity is realized, uses any combination of CDMA, FDMA, TDMA to optimize the usage of the channel, together with the combined DWDM/FS network architecture.
  • the frequency stacking system significantly increases the reverse path traffic capacity.
  • Figure 10 shows a composite RF spectrum of four upconverted return path frequency blocks (5-42 MHz).
  • a reference pilot tone is generated above the payload multiplex in order to synthesize the four-band stack.
  • the pilot tone is transmitted along with the upconverted signal and utilized in a block down-converter unit to synchronize the down-conversion, thus removing any frequency offset errors.
  • the composite RF signal is then used to drive each of the DWDM reverse path laser transmitters.
  • the DWDM laser transmitters can be either directly or externally modulated DFB laser transmitters operating in 1550-nm wavelength band.
  • multiplexer 920 optically multiplexes the signals from DWDM transmitters 910a-d on a single fiber to be routed to the headend, where the optical signal may be amplified, and is optically demultiplexed to four different optical receivers.
  • the composite output RF signal from each optical receiver is transmitted to a block down-converter unit, which extracts the four separate 5-42 MHz bands. Again, each of the high-speed data bands can be routed to return path application receivers.
  • Figure 11 illustrates the combined FSS/DWDM expansion process.
  • a single shared traditional 37 MHz segment provides 74 KHz per home (for 500 home passed node).
  • the implementation of frequency stacking (4 band) increases the shared segment to 148 Mhz thereby increasing the return bandwidth per home to 296KHz.
  • the implementation of both frequency stacking and DWDM increases the return path bandwidth segment to 32 times the return path bandwidth segment, or 1184 MHz, thereby increasing the return bandwidth per home to 2.368 MHz.
  • the architecture of the present invention provides an increased capacity in the reverse path network and is well suited to implementation into existing systems that may have fiber limitations.

Landscapes

  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Multimedia (AREA)
  • Optical Communication System (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
  • Details Of Television Systems (AREA)

Abstract

Architecture bidirectionnelle de réseau de télévision câblée à multiplexage par répartition de densité de signaux (DWDM) possédant un système d'empilage de fréquences et permettant d'augmenter la capacité du réseau dans le trajet inverse. La combinaison de multiplexage optique, mettant en application un multiplexage par répartition de densité de signaux, et de multiplexage RF, mettant en application un empilage de fréquences, augmente considérablement l'efficacité du trajet de retour dans une architecture bidirectionnelle. Les émetteurs à grille UIT et le système d'empilage de fréquences peuvent être situés au niveau des noeuds, au niveau des têtes de station primaires ou secondaires, ou bien le système d'empilage de fréquences peut se trouver au niveau du noeud et les émetteurs à grille UIT au niveau de la tête de station primaire ou secondaire.
EP00922286A 1999-04-19 2000-04-18 Architecture bidirectionnelle de reseau dwdm presentant une augmentation de capacite et un systeme d'empilage de frequences Withdrawn EP1173945A1 (fr)

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US12991299P 1999-04-19 1999-04-19
US129912P 1999-04-19
US49408300A 2000-01-28 2000-01-28
US494083 2000-01-28
PCT/US2000/010358 WO2000064087A1 (fr) 1999-04-19 2000-04-18 Architecture bidirectionnelle de reseau dwdm presentant une augmentation de capacite et un systeme d'empilage de frequences

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US6944404B2 (en) * 2000-12-11 2005-09-13 Harris Corporation Network transceiver for extending the bandwidth of optical fiber-based network infrastructure
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EP1811692B1 (fr) * 2004-11-11 2012-06-13 Nippon Telegraph And Telephone Corporation Appareil de transport optique, systeme de transmission optique, methode de transport optique et methode de transmission
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EP2301171A1 (fr) * 2008-06-30 2011-03-30 Telefonaktiebolaget L M Ericsson (PUBL) Appareil et modules pour réseau optique
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AU4249200A (en) 2000-11-02
TW468314B (en) 2001-12-11

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